The present specification generally relates to carrier implementation in communication systems and/or network deployments, such as UMTS, HSPA, LTE/LTE-A or the like. More specifically, the present specification generally relates to carrier implementation in the context of carrier aggregation (CA) techniques in such communication systems and/or network deployments, especially carrier implementation enabling energy saving at a network side (e.g. an eNodeB representing a base station or access node).
In such communication systems and/or network deployments, various reference signals are transmitted from the network side (e.g. an eNodeB representing a base station or access node) to a terminal side (e.g. an UE), not only but also in the context of carrier aggregation (CA) techniques. In 3GPP systems for example, reference signals such as CRS, CSI-RS, PSS, SSS and/or PBCH are transmitted on a carrier (potentially subject to CA) by the eNodeB and used by the UEs for one or more of time synchronization, frequency synchronization, tracking, CQI measurements, channel estimation, channel demodulation, and RRM measurements. Such reference signals, including e.g. the CRS, are typically transmitted in every TTI (e.g. in every subframe) on the carrier so as to enable proper execution of the aforementioned procedures at the UEs.
This means that, before switching off transmission of a carrier carrying such reference signals (including e.g. the CRS) for enabling energy savings at the eNodeB, the eNodeB has to make sure that there are no UEs in its coverage area, which are configured to perform any one of the aforementioned procedures on the corresponding carrier.
In practice, such requirement for carrier switch-off leads to the restrictions that the corresponding cell (i.e. the PCell on the corresponding carrier) should not be in the neighbor list of any UE, and that all SCells on the corresponding carrier should be de-configured or, alternatively, all SCells on the corresponding carrier should be deactivated and configured with a deactivated SCell measurement cycle (e.g. a measurement cycle set to infinity). These restrictions in practice mean that, even when configuring a carrier as SCell-only carrier, switching off transmission thereof is a quite heavy procedure subject to severe requirements. As a consequence, only adaptation to slow traffic variations is possible by way of such conventional carrier switch-off procedure.
In an effort to reduce signaling of reference signals in time and frequency domain (as compared to conventional and/or backward compatible carriers) for enabling energy savings at the eNodeB, it may be conceivable to reduce CRS bandwidth (i.e. a narrower CRS bandwidth than system bandwidth), to reduce frequency of CRS transmission (i.e. avoid a CRS transmission in every subframe), or to use CSI-RS instead of CRS. However, in such conceivable approaches, a reference signal for time and frequency synchronization, tracking, and RRM measurements needs to be provided. This means that the eNodeB has to continuously provide some reference signal with a given frequency and time resolution as long as there are UEs which are configured to perform any one of the aforementioned procedures on the corresponding carrier. As a consequence, practically available energy savings at the eNodeB, especially in the context of CA techniques, are quite limited.
Accordingly, any conventional and/or backward compatible carrier implementation only provides for adaptability to slow traffic variations and a limited energy savings potential.
Therefore, there is a need to provide for a configuration of carrier-related reference signal transmission, which is capable of realizing adaptability to fast traffic variations and an enhanced energy savings potential.